gocb should split its concepts of supporting and enabling.

Currently gocbcore conflates the idea of a feature being requested, a feature being supported and a feature being enabled into a singular item. These should be split up such that a developer can request a feature, have it be unsupported and disabled and relatedly allow the developer to subsequently check whether the feature is supported or not. It's possible that we can ignore the 'is it enabled' idea and allow the user to check for support after-the-fact and then relate that to whether they requested the feature. This will make it easier for people to look at what's supported without necessarily needing to enable it.